Thin film fuse phase change cell with thermal isolation pad and manufacturing method

ABSTRACT

A memory device comprising a first electrode having a top side, a second electrode having a top side and an insulating member between the first electrode and the second electrode. The insulating member has a thickness between the first and second electrodes near the top side of the first electrode and the top side of the second electrode extends outwardly from the top sides of the first and second electrodes defining a wall of insulating material having top side. A bridge of memory material crosses the insulating member over the top of the wall, and defines an inter-electrode path between the first and second electrodes across the insulating member. An array of such memory cells is provided. The bridge comprises an active layer of memory material on the top side of the wall, having at least two solid phases and a layer of thermal insulating material overlying the memory material having thermal conductivity less than a thermal conductivity of the first and second electrodes.

RELATED APPLICATIONS

This application is a divisional of copending U.S. patent applicationSer. No. 11/425,183 filed on 20 Jun. 2006, which application claims thebenefit of U.S. Provisional Application No. 60/749,843, entitled THINFILM FUSE PHASE CHANGE CELL WITH THERMAL ISOLATION PAD AND MANUFACTURINGMETHOD, filed on 13 Dec. 2005, and such applications are incorporatedherein by reference.

PARTIES TO A JOINT RESEARCH AGREEMENT

International Business Machines Corporation, a New York corporation;Macronix International Corporation, Ltd., a Taiwan corporation, andInfineon Technologies A.G., a German corporation, are parties to a JointResearch Agreement.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to high density memory devices based onphase change based memory materials, including chalcogenide basedmaterials and other materials, and to methods for manufacturing suchdevices.

2. Description of Related Art

Phase change based memory materials are widely used in read-writeoptical disks. These materials have at least two solid phases, includingfor example a generally amorphous solid phase and a generallycrystalline solid phase. Laser pulses are used in read-write opticaldisks to switch between phases and to read the optical properties of thematerial after the phase change.

Phase change based memory materials, like chalcogenide based materialsand similar materials, also can be caused to change phase by applicationof electrical current at levels suitable for implementation inintegrated circuits. The generally amorphous state is characterized byhigher resistivity than the generally crystalline state, which can bereadily sensed to indicate data. These properties have generatedinterest in using programmable resistive material to form nonvolatilememory circuits, which can be read and written with random access.

The change from the amorphous to the crystalline state is generally alower current operation. The change from crystalline to amorphous,referred to as reset herein, is generally a higher current operation,which includes a short high current density pulse to melt or breakdownthe crystalline structure, after which the phase change material coolsquickly, quenching the phase change process, allowing at least a portionof the phase change structure to stabilize in the amorphous state. It isdesirable to minimize the magnitude of the reset current used to causetransition of phase change material from crystalline state to amorphousstate. The magnitude of the reset current needed for reset can bereduced by reducing the size of the phase change material element in thecell and of the contact area between electrodes and the phase changematerial, so that higher current densities are achieved with smallabsolute current values through the phase change material element.

One direction of development has been toward forming small pores in anintegrated circuit structure, and using small quantities of programmableresistive material to fill the small pores. Patents illustratingdevelopment toward small pores include: Ovshinsky, “Multibit Single CellMemory Element Having Tapered Contact,” U.S. Pat. No. 5,687,112, issuedNov. 11, 1997; Zahorik et al., “Method of Making Chalogenide [sic]Memory Device,” U.S. Pat. No. 5,789,277, issued Aug. 4, 1998; Doan etal., “Controllable Ovonic Phase-Change Semiconductor Memory Device andMethods of Fabricating the Same,” U.S. Pat. No. 6,150,253, issued Nov.21, 2000.

Problems have arisen in manufacturing such devices with very smalldimensions, and with variations in the process that meet tightspecifications needed for large-scale memory devices. It is desirabletherefore to provide a memory cell structure having small dimensions andlow reset currents, and a method for manufacturing such structure thatmeets tight process variation specifications needed for large-scalememory devices. It is further desirable to provide a manufacturingprocess and a structure which are compatible with manufacturing ofperipheral circuits on the same integrated circuit.

SUMMARY OF THE INVENTION

A phase change random access memory PCRAM device is described suitablefor use in large-scale integrated circuits. Technology described hereinincludes a memory device comprising a first electrode having a top side,a second electrode having a top side and an insulating member betweenthe first electrode and the second electrode. The insulating memberextends above the top surfaces of the first and second electrodes toform a wall of insulating material. The bridge of memory materialcomprises three components in illustrated example, including a firstthermally insulating pad on the surface of the first electrode, a secondthermally insulating pad on the surface of the second electrode, and anarrow strip of memory material extending across the wall of insulatingmaterial. The insulating member has a thickness between the first andsecond electrodes near the top side of the first electrode and the topside of the second electrode. The thin film bridge crosses theinsulating member, and defines an inter-electrode path between the firstand second electrodes across the insulating member. The inter-electrodepath across the insulating member has a path length defined by the widthof the insulating member. For the purpose of illustration, the bridgecan be thought of as having a structure like a fuse. For the phasechange memory however, and unlike a fuse, the bridge comprises memorymaterial having at least two solid phases that are reversible, such as achalcogenide-based material or other related material, by applying acurrent through the material or applying a voltage across the first andsecond electrodes.

The volume of memory material subject to phase change can be very small,determined by the thickness of the insulating member (path length in thex-direction), the thickness of the thin film on top of the insulatingmember used to form the bridge (y-direction), and the width of thebridge orthogonal to the path length (z-direction). The thickness of theinsulating member and the thickness of the thin film of memory materialused to form the bridge are determined in embodiments of the technologyby thin film thicknesses which are not limited by the lithographicprocesses used in manufacturing the memory cell. The width of the bridgeis also smaller than a minimum feature size F that is specified for alithographic process used in patterning the layer of material inembodiments of the present invention. In one embodiment, the width ofthe bridge is defined using photoresist trimming technologies in which amask pattern is used to define a lithographical photoresist structure onthe chip having the minimum feature size F, and the photoresiststructure is trimmed by isotropic etching to achieve a feature size lessthan F. The trimmed photoresist structure is then used tolithographically transfer the more narrow pattern onto the layer ofmemory material. Also, other techniques can be used to form narrow linesof material in a layer on an integrated circuit. Accordingly, a phasechange memory cell with simple structure achieves very small resetcurrent and low power consumption, and is easily manufactured.

A method for manufacturing a memory device is also described. The methodcomprises forming an electrode layer on a substrate which comprisescircuitry made using front-end-of-line procedures. The electrode layerin this method has a top surface. The electrode layer includes a firstelectrode and a second electrode, and an insulating member between thefirst and second electrodes for each phase change memory cell to beformed. The first and second electrodes and the insulating member extendto the top surface of the electrode layer. The material of the first andsecond electrodes is etched back to form a wall on insulating materialextending above the surface of the electrodes. The method also includesforming a bridge of memory material on the top surface of the electrodelayer across the wall of insulating material in the insulating memberfor each memory cell to be formed. The bridge comprises a film of memorymaterial having a first side and a second side and contacts the firstand second electrodes on the first side. The bridge defines aninter-electrode path between the first and second electrodes across theinsulating member having a path length defined by the width of theinsulating member. In embodiments of the method, an access structureover the electrode layer is made by forming a patterned conductive layerover said bridge, and forming a contact between said first electrode andsaid patterned conductive layer.

In an embodiment of the manufacturing method, the electrode layer ismade by a process comprising a number of steps including the following:

forming a dielectric layer on a substrate;

forming a first conductive layer on the dielectric layer;

etching a pattern in the first conductive layer, the pattern includingregions between the stacks exposing the substrate, and stacks on thesubstrate including remaining portions of the dielectric layer andremaining portions of the first conductive layer, the stacks havingsidewalls;

forming a sidewall dielectric layer over the stacks and etching thesidewall dielectric layer to form sidewall spacers on the sidewalls ofthe stacks;

forming a second conductive layer over the regions between the stacks,the sidewall spacers and the stacks; and

polishing the second conductive layer, by chemical mechanical polishingor otherwise, to define the electrode layer, wherein the sidewallspacers are exposed on the top surface; and

selectively etching back the material of the first and second electrodesto expose a wall of insulating material of the sidewall spacers, whereinthe sidewall spacers and walls of insulating material act as theinsulating member, portions of the first conductive layer in the stacksare exposed on the etched back top surface and act as the firstelectrode, and portions of the second conductive layer in the regionsbetween the stacks are exposed on the etched back top surface and act asthe second electrode.

In an embodiment of the manufacturing method, the bridges of memorymaterial are made by a process comprising a number of steps includingthe following:

forming a layer of memory material on the top surface of the electrodelayer;

forming a layer of resist material over the layer of memory material;

patterning the layer of resist material using a lithographic process todefine a stripe;

trimming the width of the stripe to define a more narrow stripe ofresist material over the layer of memory material;

etching the layer of memory material which is not protected by the morenarrow stripe of resist material to form a stripe of memory material;and

patterning the stripe of memory material to define said bridge.

The method described herein for formation of the bridge, for use in amemory cell in the PCRAM, can be used to make a very small bridge forother uses. Nano-technology devices with very small bridge structuresare provided using materials other than phase change materials, likemetals, dielectrics, organic materials, semiconductors, and so on.

Other aspects and advantages of the technology described herein are setforth below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of a thin film bridge phase changememory element.

FIG. 2 illustrates an alternative embodiment of a thin film bridge phasechange memory element.

FIG. 3 illustrates a structure for a pair of phase change memoryelements with access circuitry below an electrode layer and bit linesabove the electrode layer.

FIG. 4 shows a layout or plan view for the structure illustrated in FIG.3.

FIG. 5 is a schematic diagram for a memory array comprising phase changememory elements.

FIG. 6 is a block diagram of an integrated circuit device including athin film fuse phase change memory array and other circuitry.

FIG. 7 is a cross-section of a substrate that includes access circuitryformed by front-end-of-line processes, made in a process formanufacturing a phase change memory device based on the structure shownin FIG. 3.

FIG. 8 is a cross-section showing initial steps in formation of anelectrode layer for the structure shown in FIG. 3.

FIGS. 9A and 9B show layout and cross-sectional views for patterning thestructure of FIG. 8, forming electrode stacks in the electrode layer forthe structure shown in FIG. 3.

FIG. 10 shows a cross-sectional view corresponding to steps forformation of sidewall insulators on the electrode stacks of FIG. 9B.

FIG. 11 shows a cross-sectional view corresponding to steps forformation of a layer of conductor material over the structure of FIG.10.

FIG. 12 shows a cross-sectional view corresponding to steps forpolishing the conductive material and sidewall insulators in thestructure of FIG. 11.

FIG. 13 shows a cross-sectional view corresponding to steps for etchingback the conductive material to cause insulating walls formed by thesidewall insulators to protrude from the surface of the electrode layer.

FIG. 14 shows a cross-sectional view corresponding to steps for forminga thin film layer of phase change material and a protective cap layer onthe structure of FIG. 13.

FIGS. 15A and 15B show layout and cross-sectional views for patterningthe thin film layer of phase change material of FIG. 14, forming stripsof photoresist on the phase change material.

FIGS. 16A and 16B show layout and cross-sectional views for patterningthe thin film layer of phase change material of FIG. 14, after etchingthe strips of photoresist of FIGS. 15A and 15B to form narrow strips ofphotoresist.

FIGS. 17A and 17B show layout and cross-sectional views of the strips ofphase change material after etching the thin film layer of phase changematerial according to the pattern of photoresist shown in FIGS. 16A and16B.

FIGS. 18A and 18B show layout and cross-sectional views for patterningthe strips of phase change material of FIGS. 17A and 17B, used to formbridges of phase change material on the electrode layer.

FIGS. 19A and 19B show layout and cross-sectional views of the bridgesof phase change material after etching according to the pattern of FIGS.18A and 18B.

FIG. 20 shows a cross-sectional view corresponding to steps for forminga dielectric fill layer over the structure shown in FIGS. 19A and 19B,including the electrode layer and the bridges of phase change material.

FIGS. 21A and 21B show layout and cross-sectional views after formationof conductive plugs in the dielectric fill layer contacting theelectrode layer in the structure shown in FIG. 20.

FIG. 22 shows a cross-sectional view corresponding to steps for forminga patterned conductive layer structure over the structure shown in FIGS.21A and 21B.

DETAILED DESCRIPTION

A detailed description of thin film fuse phase change memory cells,arrays of such memory cells, and methods for manufacturing such memorycells, is provided with reference to FIGS. 1-22.

FIG. 1 illustrates a basic structure of a memory cell 10 including abridge 11 of memory material on an electrode layer which comprises afirst electrode 12, a second electrode 13, and an insulating member 14between the first electrode 12 and the second electrode 13. Asillustrated, the first and second electrodes 12, 13 comprise one or morelayers of metal such as tungsten, copper, TiN, TaN or other metallicmaterials, and have top surfaces 12 a and 13 a. The insulating member 14extends above the top surfaces 12 a and 13 a of the first and secondelectrodes 12, 13 to form a wall of insulating material which has a topsurface 14 a. The bridge 11 of memory material comprises threecomponents in illustrated example, including a first thermallyinsulating pad 15 on the surface 12 a of the first electrode, a secondthermally insulating pad 16 on the surface 13 a of the second electrode,and a narrow strip 17. In the embodiment illustrated, the first andsecond thermally insulating pads 15, 16 have top surfaces which arecoplanar with the top surface 14 a of the wall of insulating material,defining a planar top surface. The narrow strip 17 of memory materiallies on the planar top surface. Contacts between the first electrode andthe bridge 11 and between the second electrode 13 and the bridge 11 aremade on the bottom side of the bridge 11 on the thermally insulatingpads 15, 16. The active region 20 of the memory material lies near thetop surface 14 a of the insulating wall in the narrow strip 17. As canbe appreciated, the active region 20 can be made extremely small in theillustrated structure, reducing the magnitude of current needed toinduce the phase changes.

In the embodiment illustrated in FIG. 1, the first and second insulatingpads 15, 16 comprise the same material as the narrow strip of memorymaterial 17. This configuration is useful when the memory material has athermal conductivity which is lower than that of the electrode material.For example, if the memory material comprises a phase change materiallike GST described below, and the electrode material comprises TiN, thenthe active region 20 in the narrow strip 17 of memory material will bethermally isolated from the electrode material by the pads 15, 16, tothe extent that the thermal conductivity is low in the memory material.In other embodiments, the thermally insulating pads 15, 16 may comprisematerials that are different from the memory material, and yet providefor electrical communication between the narrow strip 17 of memorymaterial and the electrodes 12, 13. For example, in alternativeembodiments, the thermally insulating pads may comprise a doped GST inwhich the doping material causes an even lower thermal conductivity. Thethermally insulating pads may comprise a variety of other memorymaterials, as described in more detail below. Alternatively, thethermally insulating pads may comprise metal oxides, such as tin oxidesSnO_(x), indium oxides InO_(x) or titanium oxides TiO_(x), so long asthe material provides electrical communication between the bridge ofmemory material and the electrode materials, while providing thermalinsulation better than the thermal insulation of the metal electrodes.

FIG. 2 shows an alternative implementation of a basic structure of amemory cell 10, using like reference numerals for like components. Inthe embodiment shown in FIG. 2, the thermally insulating pads comprisenarrow structures 18, 19, rather than the broader structures formingpads 15, 16 shown in FIG. 1. In the embodiment shown in FIG. 2, theprocess of etching the narrow strip 17 of memory material can be appliedto also define the extent of the thermally insulating pads.

Access circuitry can be implemented to contact the first electrode 12and the second electrode 13 in a variety of configurations forcontrolling the operation of the memory cell, so that it can beprogrammed to set the bridge 11 in one of the two solid phases that canbe reversibly implemented using the memory material. For example, usinga chalcogenide-based phase change memory material, the memory cell maybe set to a relatively high resistivity state in which at least aportion of the bridge in the current path is in an amorphous state, anda relatively low resistivity state in which most of the bridge in thecurrent path is in a crystalline state.

FIG. 2 illustrates important dimensions of the memory cell 10. Thelength L (x-dimension) of the active region 20 is defined by thethickness of the insulating member 14, between the first electrode 12and the second electrode 13. This length L can be controlled bycontrolling the width of the insulating member 14 at surface 14 a inembodiments of the memory cell. In representative embodiments, the widthof the insulating member 14 can be established using a thin filmdeposition technique to form a thin sidewall dielectric on the side ofan electrode stack. Thus, embodiments of the memory cell have a channellength L less than 100 nm. Other embodiments have a channel length L ofabout 40 nm or less. In yet other embodiments, the channel length isless than 20 nm. It will be understood that the channel length L can beeven smaller than 20 nm, using thin-film deposition techniques such asatomic layer deposition and the like, according to the needs of theparticular application. The wall of insulating material may extendupward from the surfaces of the electrodes 12, 13 by a range of about 50to 100 nanometers, for example, in some embodiments of the memory cell,which in turn determines the thicknesses of the insulating pads.

Likewise, the bridge thickness T1 (y-dimension) can be very small inembodiments of the memory cell. This bridge thickness T1 can beestablished using a thin film deposition technique on the top surfacesof the first electrode 12 or thermally insulating pad 18, top 14 a ofthe insulating wall on insulating member 14, and second electrode 13 orthermally insulating pad 19. Thus, embodiments of the memory cell have abridge thickness T1 about 50 nm or less. Other embodiments of the memorycell have a bridge thickness of about 20 nm or less. In yet otherembodiments, the bridge thickness T1 is about 10 nm or less. It will beunderstood that the bridge thickness T1 can be even smaller than 10 nm,using thin film deposition techniques such as atomic layer depositionand the like, according to the needs of the particular application, solong as the thickness is sufficient for the bridge to perform itspurpose as memory element. Thickness T1 of the layer 17 of phase changematerial over the top surface 14 a of the insulating wall 14 can bedifferent than the thickness T2 of the pads, which corresponds in FIG. 2with the distance that the insulating wall 14 extends above theelectrodes 12 and 13. In some embodiments, the thickness T2 is greaterthan the thickness T1, including for example 2 to 5 times greater.

As illustrated in FIG. 2, the bridge width W (z-dimension) is likewisevery small. This bridge width W is implemented in preferred embodiments,so that it has a width less than 100 nm. In some embodiments, the bridgewidth W is about 40 nm or less.

Embodiments of the memory cell include phase change based memorymaterials, including chalcogenide based materials and other materials,for the bridge 11. Chalcogens include any of the four elements oxygen(O), sulfur (S), selenium (Se), and tellurium (Te), forming part ofgroup VI of the periodic table. Chalcogenides comprise compounds of achalcogen with a more electropositive element or radical. Chalcogenidealloys comprise combinations of chalcogenides with other materials suchas transition metals. A chalcogenide alloy usually contains one or moreelements from column six of the periodic table of elements, such asgermanium (Ge) and tin (Sn). Often, chalcogenide alloys includecombinations including one or more of antimony (Sb), gallium (Ga),indium (In), and silver (Ag). Many phase change based memory materialshave been described in technical literature, including alloys of: Ga/Sb,In/Sb, In/Se, Sb/Te, Ge/Te, Ge/Sb/Te, In/Sb/Te, Ga/Se/Te, Sn/Sb/Te,In/Sb/Ge, Ag/In/Sb/Te, Ge/Sn/Sb/Te, Ge/Sb/Se/Te and Te/Ge/Sb/S. In thefamily of Ge/Sb/Te alloys, a wide range of alloy compositions may beworkable. The compositions can be characterized asTe_(a)Ge_(b)Sb_(100−(a+b)). One researcher has described the most usefulalloys as having an average concentration of Te in the depositedmaterials well below 70%, typically below about 60% and ranged ingeneral from as low as about 23% up to about 58% Te and most preferablyabout 48% to 58% Te. Concentrations of Ge were above about 5% and rangedfrom a low of about 8% to about 30% average in the material, remaininggenerally below 50%. Most preferably, concentrations of Ge ranged fromabout 8% to about 40%. The remainder of the principal constituentelements in this composition was Sb. These percentages are atomicpercentages that total 100% of the atoms of the constituent elements.(Ovshinsky '112 patent, cols 10-11.) Particular alloys evaluated byanother researcher include Ge₂Sb₂Te₅, GeSb₂Te₄ and GeSb₄Te₇ (NoboruYamada, “Potential of Ge—Sb—Te Phase-Change Optical Disks forHigh-Data-Rate Recording”, SPIE v. 3109, pp. 28-37 (1997).) Moregenerally, a transition metal such as chromium (Cr), iron (Fe), nickel(Ni), niobium (Nb), palladium (Pd), platinum (Pt) and mixtures or alloysthereof may be combined with Ge/Sb/Te to form a phase change alloy thathas programmable resistive properties. Specific examples of memorymaterials that may be useful are given in Ovshinsky '112 at columns11-13, which examples are hereby incorporated by reference.

Phase change alloys are capable of being switched between a firststructural state in which the material is in a generally amorphous solidphase, and a second structural state in which the material is in agenerally crystalline solid phase in its local order in the activechannel region of the cell. These alloys are at least bistable. The termamorphous is used to refer to a relatively less ordered structure, moredisordered than a single crystal, which has the detectablecharacteristics such as higher electrical resistivity than thecrystalline phase. The term crystalline is used to refer to a relativelymore ordered structure, more ordered than in an amorphous structure,which has detectable characteristics such as lower electricalresistivity than the amorphous phase. Typically, phase change materialsmay be electrically switched between different detectable states oflocal order across the spectrum between completely amorphous andcompletely crystalline states. Other material characteristics affectedby the change between amorphous and crystalline phases include atomicorder, free electron density and activation energy. The material may beswitched either into different solid phases or into mixtures of two ormore solid phases, providing a gray scale between completely amorphousand completely crystalline states. The electrical properties in thematerial may vary accordingly.

Phase change alloys can be changed from one phase state to another byapplication of electrical pulses. It has been observed that a shorter,higher amplitude pulse tends to change the phase change material to agenerally amorphous state. A longer, lower amplitude pulse tends tochange the phase change material to a generally crystalline state. Theenergy in a shorter, higher amplitude pulse is high enough to allow forbonds of the crystalline structure to be broken and short enough toprevent the atoms from realigning into a crystalline state. Appropriateprofiles for pulses can be determined, without undue experimentation,specifically adapted to a particular phase change alloy. In followingsections of the disclosure, the phase change material is referred to asGST, and it will be understood that other types of phase changematerials can be used. A material useful for implementation of a PCRAMdescribed herein is Ge₂Sb₂Te₅.

Other programmable resistive memory materials may be used in otherembodiments of the invention, including N₂ doped GST, Ge_(x)Sb_(y), orother material that uses different crystal phase changes to determineresistance; Pr_(x)Ca_(y)MnO₃, PrSrMnO₃, ZrOx, or other material thatuses an electrical pulse to change the resistance state;7,7,8,8-tetracyanoquinodimethane (TCNQ), methanofullerene 6,6-phenylC61-butyric acid methyl ester (PCBM), TCNQ-PCBM, Cu-TCNQ, Ag-TCNQ,C60-TCNQ, TCNQ doped with other metal, or any other polymer materialthat has bistable or multi-stable resistance state controlled by anelectrical pulse.

The following are short summaries describing four types of resistivememory materials useful in alternative embodiments. The first type ischalcogenide material, such as Ge_(x)Sb_(y)Te_(z) where x:y:z=2:2:5, orother compositions with x: 0˜5; y: 0˜5; z: 0˜10. GeSbTe with doping,such as N—, Si—, Ti—, or other element doping is alternatively used.

An exemplary method for forming chalcogenide material usesPVD-sputtering or magnetron-sputtering method with source gas(es) of Ar,N₂, and/or He, etc. at the pressure of 1 mTorr˜100 mTorr. The depositionis usually done at room temperature. A collimater with an aspect ratioof 1˜5 can be used to improve the fill-in performance. To improve thefill-in performance, a DC bias of several tens of volts to severalhundreds of volts is also used. On the other hand, the combination of DCbias and the collimater can be used simultaneously.

A post-deposition annealing treatment in vacuum or in an N₂ ambient isoptionally performed to improve the crystallize state of chalcogenidematerial. The annealing temperature typically ranges from 100° C. to400° C. with an anneal time of less than 30 minutes.

The thickness of chalcogenide material depends on the design of cellstructure. In general, a chalcogenide material with thickness of higherthan 8 nm can have a phase change characterization so that the materialexhibits at least two stable resistance states.

A second type of memory material suitable for use in embodiments iscolossal magnetoresistance (“CMR”) material, such as Pr_(x)Ca_(y)MnO₃where x:y=0.5:0.5, or other compositions with x: 0˜1; y: 0˜1. CMRmaterial that includes Mn oxide is alternatively used.

An exemplary method for forming CMR material uses PVD sputtering ormagnetron-sputtering method with source gases of Ar, N₂, O₂, and/or He,etc. at the pressure of 1 mTorr˜100 mTorr. The deposition temperaturecan range from room temperature to ˜600° C., depending on the postdeposition treatment condition. A collimater with an aspect ratio of 1˜5can be used to improve the fill-in performance. To improve the fill-inperformance, the DC bias of several tens of volts to several hundreds ofvolts is also used. On the other hand, the combination of DC bias andthe collimater can be used simultaneously. A magnetic field of severaltens of Gauss to as much as a Tesla (10,000 Gauss) may be applied toimprove the magnetic crystallized phase.

A post-deposition annealing treatment in vacuum or in an N₂ ambient orO₂/N₂ mixed ambient is optionally used to improve the crystallized stateof CMR material. The annealing temperature typically ranges from 400° C.to 600° C. with an anneal time of less than 2 hours.

The thickness of CMR material depends on the design of the cellstructure. The CMR thickness of 10 nm to 200 nm can be used for the corematerial. A buffer layer of YBCO (YBaCuO₃, which is a type of hightemperature superconductor material) is often used to improve thecrystallized state of CMR material. The YBCO is deposited before thedeposition of CMR material. The thickness of YBCO ranges from 30 nm to200 nm.

A third type of memory material is two-element compounds, such asNi_(x)O_(y); Ti_(x)O_(y); Al_(x)O_(y); W_(x)O_(y); Zn_(x)O_(y);Zr_(x)O_(y); Cu_(x)O_(y); etc, where x:y=0.5:0.5, or other compositionswith x: 0˜1; y: 0˜1. An exemplary formation method uses a PVD sputteringor magnetron-sputtering method with reactive gases of Ar, N₂, O₂, and/orHe, etc. at the pressure of 1 mTorr˜100 mTorr, using a target of metaloxide, such as Ni_(x)O_(y); Ti_(x)O_(y); Al_(x)O_(y); W_(x)O_(y);Zn_(x)O_(y); Zr_(x)O_(y); Cu_(x)O_(y); etc. The deposition is usuallydone at room temperature. A collimater with an aspect ratio of 1˜5 canbe used to improve the fill-in performance. To improve the fill-inperformance, the DC bias of several tens of volts to several hundreds ofvolts is also used. If desired, the combination of DC bias and thecollimater can be used simultaneously.

A post-deposition annealing treatment in vacuum or in an N₂ ambient orO₂/N₂ mixed ambient is optionally performed to improve the oxygendistribution of metal oxide. The annealing temperature ranges from 400°C. to 600° C. with an anneal time of less than 2 hours.

An alternative formation method uses a PVD sputtering ormagnetron-sputtering method with reactive gases of Ar/O₂, Ar/N₂/O₂, pureO₂, He/O₂, He/N₂/O₂ etc. at the pressure of 1 mTorr˜100 mTorr, using atarget of metal oxide, such as Ni, Ti, Al, W, Zn, Zr, or Cu etc. Thedeposition is usually done at room temperature. A collimater with anaspect ratio of 1˜5 can be used to improve the fill-in performance. Toimprove the fill-in performance, a DC bias of several tens of volts toseveral hundreds of volts is also used. If desired, the combination ofDC bias and the collimater can be used simultaneously.

A post-deposition annealing treatment in vacuum or in an N₂ ambient orO₂/N₂ mixed ambient is optionally performed to improve the oxygendistribution of metal oxide. The annealing temperature ranges from 400°C. to 600° C. with an anneal time of less than 2 hours.

Yet another formation method uses oxidation by a high temperatureoxidation system, such as a furnace or a rapid thermal pulse (“RTP”)system. The temperature ranges from 200° C. to 700° C. with pure O₂ orN₂/O₂ mixed gas at a pressure of several mTorr to 1 atm. The time canrange several minute to hours. Another oxidation method is plasmaoxidation. An RF or a DC source plasma with pure O₂ or Ar/O₂ mixed gasor Ar/N₂/O₂ mixed gas at a pressure of 1 mTorr to 100 mTorr is used tooxidize the surface of metal, such as Ni, Ti, Al, W, Zn, Zr, or Cu etc.The oxidation time ranges several seconds to several minutes. Theoxidation temperature ranges from room temperature to 300° C., dependingon the degree of plasma oxidation.

A fourth type of memory material is a polymer material, such as TCNQwith doping of Cu, C₆₀, Ag etc. or PCBM-TCNQ mixed polymer. Oneformation method uses evaporation by thermal evaporation, e-beamevaporation, or molecular beam epitaxy (“MBE”) system. A solid-stateTCNQ and dopant pellets are co-evaporated in a single chamber. Thesolid-state TCNQ and dopant pellets are put in a W-boat or a Ta-boat ora ceramic boat. A high electrical current or an electron-beam is appliedto melt the source so that the materials are mixed and deposited onwafers. There are no reactive chemistries or gases. The deposition isdone at a pressure of 10⁻⁴ Torr to 10⁻¹⁰ Torr. The wafer temperatureranges from room temperature to 200° C.

A post-deposition annealing treatment in vacuum or in an N₂ ambient isoptionally performed to improve the composition distribution of polymermaterial. The annealing temperature ranges from room temperature to 300°C. with an anneal time of less than 1 hour.

Another technique for forming a layer of polymer-based memory materialis to use a spin-coater with doped-TCNQ solution at a rotation of lessthan 1000 rpm. After spin-coating, the wafer is held (typically at roomtemperature or temperature less than 200° C.) for a time sufficient forsolid-state formation. The hold time ranges from several minutes todays, depending on the temperature and on the formation conditions.

FIG. 3 depicts a structure for PCRAM cells such as cells described withreference to FIGS. 1 and 2. The cells are formed on a semiconductorsubstrate 21. Isolation structures such as shallow trench isolation STIdielectrics (not shown) isolate pairs of rows of memory cell accesstransistors. The access transistors are formed by n-type terminal 26acting as a common source region and n-type terminals 25 and 27 actingas drain regions in a p-type substrate 21. Polysilicon word lines 23 and24 form the gates of the access transistors. A dielectric fill layer(not illustrated) is formed over the polysilicon word lines. The layeris patterned and conductive structures, including common source line 28and plug structures 29 and 30 are formed. The conductive material can betungsten or other materials and combinations suitable for the plug andlines structures. The common source line 28 contacts the source terminal26, and acts as a common source line along a row in the array. The plugstructures 29 and 30 contact the drain terminals 25 and 27,respectively. The fill layer (not shown), the common source line 28 andthe plug structures 29 and 30, have a generally planar top surface,suitable for formation of an electrode layer 31.

The electrode layer 31 includes electrode members 32, 33 and 34, whichare separated from one another by an insulating member includinginsulating walls 35 a and 35 b formed for example by a sidewall processas described below, and base member 39. The base member 39 can bethicker than the fences 35 a, 35 b in embodiments of the structure, andseparates the electrode member 33 from the common source line 28. Forexample the base member can be for instance, 80 to 140 nm thick whilethe fences are much narrower, as needed to reduce capacitive couplingbetween the source line 28 and the electrode member 33. The fences 35 a,35 b comprise a thin film dielectric material on the sidewalls ofelectrode members 32, 34 in the illustrated embodiment, with a thicknessat the surface of the electrode layer 31 determined by the thin filmthickness on the sidewalls.

A thin film bridge 36 of memory material, such as GST, overlies theelectrode layer 31 on one side traversing across the top of insulatingwall 35 a, forming a first memory cell, and a thin film bridge 37 ofmemory material, such as GST, overlies the electrode layer 31 on anotherside traversing across the top of insulating wall 35 b, forming a secondmemory cell. As described above with respect to FIG. 1, the bridges 36and 37 include thermally insulating pads in contact with electrodemembers 32, 33, 34, and respective narrow strips overlying the pads andthe insulating walls.

A dielectric fill layer (not illustrated) overlies the thin film bridges36, 37. The dielectric fill layer comprises silicon dioxide, apolyimide, silicon nitride or other dielectric fill materials. Inembodiments, the fill layer comprises a relatively good insulator forheat as well as for electricity, providing thermal and electricalisolation for the bridges. Tungsten plug 38 contacts the electrodemember 33. A patterned conductive layer 40, comprising metal or otherconductive material, including bit lines in an array structure, overliesthe dielectric fill layer, and contacts the plug 38 to establish accessto the memory cells corresponding to the thin film bridge 36 and thethin film bridge 37.

FIG. 4 shows the structure above the semiconductor substrate layer 21 ofFIG. 3 in layout view. Thus, the word lines 23 and 24 are laid outsubstantially parallel to the common source line 28, along those in anarray of memory cells. Plugs 29 and 30 contact terminals of accesstransistors in the semiconductor substrate and the underside ofelectrode members 32 and 34 respectively. Thin film bridges 36 and 37 ofmemory material overlie the electrode members 32, 33 and 34, and theinsulating fences 35 a, 35 b separate the electrode members. Thermallyinsulating pads between the narrow strips of memory material and thecontacts are not shown in FIG. 4 to simplify the layout drawing, but areincluded as discussed above. Plug 38 contacts the electrode member 33between the bridges 36 and 37 and the underside of a metal bit line 41(transparent in FIG. 4) in the patterned conductive layer 40. Metal bitline 42 (not transparent) is also illustrated in FIG. 4 to emphasize thearray layout of the structure.

In operation, access to the memory cell corresponding with bridge 36 isaccomplished by applying a control signal to the word line 23, whichcouples the common source line 28 via terminal 25, plug 29, andelectrode member 32 to the thin-film bridge 36. Electrode member 33 iscoupled via the contact plug 38 to a bit line in the patternedconductive layer 40. Likewise, access to the memory cell correspondingwith bridge 37 is accomplished by applying a control signal to the wordline 24.

It will be understood that a wide variety of materials can be utilizedin implementation of the structure illustrated in FIGS. 3 and 4. Forexample, copper metallization can be used. Other types of metallization,including aluminum, titanium nitride, and tungsten based materials canbe utilized as well. Also, non-metal conductive material such as dopedpolysilicon can be used. The electrode material in the illustratedembodiment is preferably TiN or TaN. Alternatively, the electrodes maybe TiAlN or TaAlN, or may comprise, for further examples, one or moreelements selected from the group consisting of Ti, W, Mo, Al, Ta, Cu,Pt, Ir, La, Ni, and Ru and alloys thereof. The inter-electrode fencemembers 35 a, 35 b may be silicon oxide, silicon oxynitride, siliconnitride, Al₂O₃, or other low K dielectrics. Alternatively, theinter-electrode insulating layer may comprise one or more elementsselected from the group consisting of Si, Al, F, N, O, and C.

FIG. 5 is a schematic illustration of a memory array, which can beimplemented as described with reference to FIGS. 3 and 4. Thus,reference numerals for elements of FIG. 5 match corresponding elementsin the structure of FIGS. 3 and 4. It will be understood that the arraystructure illustrated in FIG. 5 can be implemented using other cellstructures. In a schematic illustration of FIG. 5, the common sourceline 28, the word line 23 and the word line 24 are arranged generallyparallel in the Y-direction. Bit lines 41 and 42 are arranged generallyparallel in the X-direction. Thus, a Y-decoder and a word line driver inblock 45 are coupled to the word lines 23, 24. An X-decoder and set ofsense amplifiers in block 46 are coupled to the bit lines 41 and 42. Thecommon source line 28 is coupled to the source terminals of accesstransistors 50, 51, 52 and 53. The gate of access transistor 50 iscoupled to the word line 23. The gate of access transistor 51 is coupledto the word line 24. The gate of access transistor 52 is coupled to theword line 23. The gate of access transistor 53 is coupled to the wordline 24. The drain of access transistor 50 is coupled to the electrodemember 32 for bridge 36, which is in turn coupled to electrode member34. Likewise, the drain of access transistor 51 is coupled to theelectrode member 33 for bridge 37, which is in turn coupled to theelectrode member 34. The electrode member 34 is coupled to the bit line41. For schematic purposes, the electrode member 34 is illustrated atseparate locations on the bit line 41. It will be appreciated thatseparate electrode members can be utilized for the separate memory cellbridges in other embodiments. Access transistors 52 and 53 are coupledto corresponding memory cells as well on line 42. It can be seen thatthe common source line 28 is shared by two rows of memory cells, where arow is arranged in the Y-direction in the illustrated schematic.Likewise, the electrode member 34 is shared by two memory cells in acolumn in the array, where a column is arranged in the X-direction inthe illustrated schematic.

FIG. 6 is a simplified block diagram of an integrated circuit accordingto an embodiment of the present invention. The integrated circuit 75includes a memory array 60 implemented using thin film fuse phase changememory cells with thermally insulating pads, on a semiconductorsubstrate. A row decoder 61 is coupled to a plurality of word lines 62,and arranged along rows in the memory array 60. A column decoder 63 iscoupled to a plurality of bit lines 64 arranged along columns in thememory array 60 for reading and programming data from the thin filmphase change memory cells in the array 60. Addresses are supplied on bus65 to column decoder 63 and row decoder 61. Sense amplifiers and data-instructures in block 66 are coupled to the column decoder 63 via data bus67. Data is supplied via the data-in line 71 from input/output ports onthe integrated circuit 75 or from other data sources internal orexternal to the integrated circuit 75, to the data-in structures inblock 66. In the illustrated embodiment, other circuitry 74 is includedon the integrated circuit, such as a general purpose processor orspecial purpose application circuitry, or a combination of modulesproviding system-on-a-chip functionality supported by the thin film fusephase change memory cell array. Data is supplied via the data-out line72 from the sense amplifiers in block 66 to input/output ports on theintegrated circuit 75, or to other data destinations internal orexternal to the integrated circuit 75.

A controller implemented in this example using bias arrangement statemachine 69 controls the application of bias arrangement supply voltages68, such as read, program, erase, erase verify and program verifyvoltages. The controller can be implemented using special-purpose logiccircuitry as known in the art. In alternative embodiments, thecontroller comprises a general-purpose processor, which may beimplemented on the same integrated circuit, which executes a computerprogram to control the operations of the device. In yet otherembodiments, a combination of special-purpose logic circuitry and ageneral-purpose processor may be utilized for implementation of thecontroller.

FIG. 7 illustrates a structure 99 after front-end-of-line processing,forming the standard CMOS components in the illustrated embodimentcorresponding to the word lines, the source line, and the accesstransistors in the array shown in FIG. 7. In FIG. 7, source line 106overlies doped region 103 in the semiconductor substrate, where thedoped region 103 corresponds with the source terminal of a first accesstransistor on the left in the figure, and of a second access transistoron the right in the figure. In this embodiment, the source line 106extends to the top surface of the structure 99. In other embodiments thesource line does not extend all the way to the surface. Doped region 104corresponds with the drain terminal of the first access transistor. Aword line including polysilicon 107, and silicide cap 108, acts as thegate of the first access transistor. Dielectric layer 109 overlies thepolysilicon 107 and silicide cap 108. Plug 110 contacts doped region104, and provides a conductive path to the surface of the structure 99for contact to a memory cell electrode as described below. The drainterminal of the second access transistor is provided by doped region105. A word line including polysilicon line 111, and the silicide cap(not labeled) acts as the gate for the second access transistor. Plug112 contacts doped region 105 and provides a conductive path to the topsurface of the structure 99 for contact to a memory cell electrode asdescribed below. Isolation trenches 101 and 102 separate thetwo-transistor structure coupled to the plugs 110 and 112, from adjacenttwo-transistor structures. On the left, doped region 115, word linepolysilicon 117 and plug 114 are shown. On the right, doped region 116,word line polysilicon 118 and plug 113 are shown. The structure 99illustrated in FIG. 7 provides a substrate for formation of memory cellcomponents, including the first and second electrodes, and the bridge ofmemory material, as described in more detail below.

FIG. 8 illustrates a next stage in the process, in which a thindielectric layer 120 comprising silicon nitride SiN or other dielectricmaterial, such as silicon dioxide, silicon oxynitride, aluminum oxide,and the like, is formed on the surface of the structure 99. Then a layer121 of conductive electrode material such as titanium nitride TiN, orother suitable conductive material, such as TaN, aluminum alloys, copperalloys, doped polysilicon, etc., is formed on the dielectric layer 120.

FIGS. 9A and 9B illustrate a next stage in the process, in which theconductive electrode layer 121 and the dielectric layer 120 arepatterned to define electrode stacks 130, 131 and 132 on the surface ofthe structure 99 (130 a, 131 a, 132 a in FIG. 9A. In an embodiment, theelectrode stacks are defined by a mask lithographic step that produces apatterned layer of photoresist, followed by dimension measurement andverification steps known in the art, and then etching of the TiN and SiNused for formation of the layers 121 and 120. The stacks have sidewalls133 and 134.

FIG. 10 illustrates a next stage in the process, in which dielectricsidewalls 140, 141, 142 and 143 are formed on the sidewalls of thestacks 130, 131, 132, by forming a thin film dielectric layer (notshown) that is conformal with the stacks and the sidewalls of thestacks, and then anisotropically etching the thin film dielectric toremove it from the regions between the stacks and on the surfaces of thestacks, while remaining on the sidewalls. In embodiments of the process,the material used for formation of the sidewalls 140, 141, 142 and 143comprises SiN or other dielectric material, such as silicon dioxide,silicon oxynitride, aluminum oxide, and the like.

FIG. 11 illustrates a next stage in the process, in which a secondelectrode material layer 150 is formed over the stacks 130, 131 132 andthe sidewalls 140, 141, 142, 143. The electrode material layer 150comprises TiN or other suitable conductive material, such as TaN,aluminum alloys, copper alloys, doped polysilicon, etc.

FIG. 12 illustrates a next stage in the process, in which the secondelectrode material layer 150, the sidewalls 140, 141, 142, 143 and thestacks 130, 131, 132 are etched and planarized to define an electrodelayer over the substrate provided by structure 99. Embodiments of theprocess for polishing include a chemical mechanical polishing process,followed by brush clean and liquid and or gas clean procedures, as knownin the art. The electrode layer includes electrode members 160, 161,162, and insulating members 163 and 164 in between them. The electrodelayer in the illustrated embodiment has a substantially planar topsurface. In the embodiment shown, the insulating members 163 and 164comprise portions of a structure which also extends beneath electrodemember 161, isolating it from the source line. Other example structuresmay use different materials for the electrode members and insulatingmembers.

FIG. 13 illustrates a next stage in the process, in which the electrodematerial of electrode members 160, 161, 162 is etched back slightly,revealing insulating walls 163, 164 extending 10 nm to 100 nm, forexample, above the surfaces of the electrode members 160, 161, 162.

FIG. 14 illustrates a next stage in the process, in which a thin filmlayer 170 of a phase change based memory material is formed on thesubstantially planar top surface of the electrode layer. The memorymaterial is deposited using sputtering without collimation at about 250degrees C. This results in a thin film having a thickness of about 60nanometers or less on top of insulating walls 163, 164, when usingGe₂Sb₂Te₅ as the phase change memory material. Embodiments involvesputtering the entire wafer to thickness of about 40 nanometers on theflat surfaces. The thin film layer 170 has a thickness less than 100 nmin some embodiments, and more preferably 40 nm or less. In embodimentsof the memory device, the thin film layer 170 has a thickness of lessthan 20 nm, such as 10 nm on top of insulating walls 163, 164. Afterforming the thin film layer 170, a protective cap layer 171 is formed.The protective cap layer 171 comprises a low-temperature depositedsilicon dioxide or other dielectric material formed over the thin filmlayer 170. The protective cap layer 171 is preferably a good electricalinsulator and a good thermal insulator, and protects the memory materialfrom exposure in subsequent steps, such as photoresist stripping stepswhich can damage the material. The process involves formation of alow-temperature liner dielectric, such as a silicon nitride layer orsilicon oxide layer, using a process temperature less than about 200degrees C. One suitable process is to apply silicon dioxide using PECVD.After formation of the protective cap layer 171, a dielectric fill overthe memory material can be implemented using a higher temperatureprocess such as high-density plasma HDP CVD. In the illustratedembodiment, the material for the thermally insulating pads and for thenarrow strip on the bridges of memory material is deposited in a singlestep. In alternative approaches, the material for the thermallyinsulating pads may be first deposited, followed by a step forplanarizing the resulting structure, and then by a second depositionstep for the material to be used on the narrow bridges.

FIGS. 15A and 15B illustrate a next stage in the process, in which aphotoresist layer 180 is formed and patterned in a mask lithographicprocess to define strips 180 a, 180 b over the thin film layer 170 andprotective cap layer 171. As seen in FIG. 16A, the insulating members163 and 164 are exposed between the strips 180 a, 180 b of photoresist.The strips of photoresist are made as narrow as possible according tothe lithographic process applied. For example, the strips have a widthequal to the minimum feature size F for the lithographic process used,where the minimum feature size for a process may be on the order of 0.2microns (200 nm), 0.14 microns, or 0.09 microns in current masklithographic processes. Obviously, embodiments of the process can beadapted to narrower minimum feature sizes as lithographic processesadvance.

FIGS. 16A and 16B illustrate a next stage in the process, in which thephotoresist strips 180 a, 180 b of FIG. 15A are trimmed to form morenarrow photoresist strips 190 a, 190 b. As shown in FIG. 16B, thetrimmed photoresist 190 is also thinner than the photoresist layer 180of FIG. 15B. In one embodiment, the photoresist strips are trimmed byisotropic etching using a reactive ion etch process or otherwise. Theetching trims the photoresist strips to more narrow line widths.Embodiments of the more narrow photoresist strips 190 a, 190 b are lessthan 100 nm wide. In other embodiments the more narrow photoresiststrips 190 a, 190 b are about 40 nm or less wide. Photoresist trimmingis applied using an oxide plasma to isotropically etch the photoresist,which trims its width and thickness down to a width of for example about40 nanometers in a 0.09 micron (90 nanometer) minimum feature sizelithographic process environment. In an alternative, a hard mask layer,such as a low temperature deposited layer of SiN or SiO₂ can be put onthe bottom of the photoresist pattern to prevent etching damage of thememory material during the photoresist stripping process.

FIGS. 17A and 17B illustrate a next stage in the process, in which themore narrow photoresist strips 190 a, 190 b are used for an etch mask,and the thin film layer 200 of memory material is etched tolithographically define strips 200 a, 200 b of memory material, with orwithout the protective cap layer 201 including the pad and the strips ofa memory cell as shown in FIG. 2. As shown, the strips 200 a, 200 b spanacross the insulating members 163, 164, and the electrode members in theelectrode layer. In embodiments of the process the memory materialcomprises a GST chalcogenide based material, and is etched using forexample, a chlorine-based or fluorine-based, reactive ion etchingprocess.

FIGS. 18A and 18B illustrate a next stage in the process, in whichanother photoresist layer 210, 211, 212 is formed and patterned todefine photoresist structures 210 a, 210 b, 211 a, 211 b, 212 a and 212b. The cell structures correspond with pairs of memory cells asdescribed below. The cell structures are wider than the strips 200 a,200 b shown in FIG. 17A of memory material because they have a widthequal to the width achieved using the lithographic process applied inthe manufacturing process, such as a photomask based lithographicprocess, without trimming. Thus, the width in some embodiments is equalto the minimum feature size F for the lithographic process applied informing the layer.

FIGS. 19A and 19B illustrate a next stage in the process, in which thephotoresist structures 210 a, 210 b, 211 a, 211 b, 212 a and 212 b areused as etch masks to define cell structures (220 a, 220 b, 221 a, 221b, 222 a and 222 b in FIG. 19A, 220, 221, 222, in FIG. 19B) by etchingtrenches 225, 226 to the isolation dielectric structures in thestructure 99, and the trenches 227 between columns of cells orthogonalto the word lines. The cell structure 220 a includes a first electrodemember 215, a second electrode member 216 and a third electrode member217. Insulating member 163 separates the first electrode member 215 fromthe second electrode member 216. Insulating member 164 separates thefirst electrode member 215 from the third electrode member 217. A bridge218 of memory material (including thermally insulating pads and narrowstrips as described with reference to FIG. 2) overlies the electrodemembers 215, 216 and 217 and the insulating members 163, 164 toestablish two memory cells on the structure 220.

FIG. 20 illustrates a next stage in the process, in which a dielectricfill layer 230 with a planar top surface is formed over the electrodestructures and fills the gaps and trenches between them. In anembodiment of the process, the fill layer 230 is formed by high-densityplasma HDP chemical vapor deposition CVD, followed by chemicalmechanical polishing and cleaning. The dielectric fill may comprisesilicon oxides, silicon nitrides, and other insulating materials,preferably having good thermal as well as electrical insulatingproperties.

In some embodiments a structure for thermally insulating the bridges isprovided, in addition to or instead of the dielectric fill layer. In oneexample, the thermally insulating structure is formed by providing a caplayer of thermally insulating material over the bridges (218) andoptionally over the electrode layer, before applying the dielectricfill. In one example, the thermally insulating structure is formed byproviding a cap layer of thermally insulating material over the bridges(218) and optionally over the electrode layer, before applying thedielectric fill. Representative materials for the layer of thermallyinsulating material include materials that are a combination of theelements silicon Si, carbon C, oxygen O, fluorine F, and hydrogen H.Examples of thermally insulating materials which are candidates for usefor the thermally insulating cap layer include SiO₂, SiCOH, polyimide,polyamide, and fluorocarbon polymers, selected so that the material hasa lower thermal conductivity that the dielectric fill layer to bedeposited over it. When the overlying material is SiO2, the thermallyinsulating material should have a thermal conductivity less than that ofSiO2, or less than about 0.014 J/cm*degK*sec. In other preferredembodiments, the thermal insulator has a thermal conductivity less thanthat of the amorphous state of the phase change material, or less thanabout 0.003 J/cm*K*sec for a phase change material comprising GST. Manylow-K materials, where low-K materials have permitivity less than thatof SiO₂, are suitable thermal insulators. Examples of materials whichare candidates for use for the thermally insulating cap layer includefluorinated SiO2, silsesquioxane, polyarylene ethers, parylene,fluoro-polymers, fluorinated amorphous carbon, diamond like carbon,porous silica, mesoporous silica, porous silsesquioxane, porouspolyimide, and porous polyarylene ethers. In other embodiments, thethermally insulating structure comprises a gas-filled void in thedielectric fill formed over the bridge for thermal insulation. A singlelayer or combination of layers can provide thermal and electricalinsulation.

FIGS. 21A and 21B illustrate a next stage in the process, in which vias(not shown) are etched in the fill layer 230 to the electrode material,through the memory material and the fill. The via etch process may be asingle anisotropic etch for both the fill and the memory material, or atwo step process first etching the fill material with a first etchchemistry, and second etching the memory material with a second etchchemistry. After forming the vias, the vias are filled with tungsten orother conductive material, to form plugs 240 (240 a, 240 b in FIG. 21A),241 and 242 contacting the first electrode member (e.g. member 215) inthe electrode structures, for electrical communication with circuitryabove the electrode layer. In embodiments of the process, the vias arelined with a diffusion barrier layer and/or an adhesion layer, as knownin the art, and filled with tungsten or other suitable conductivematerial. The structure is then planarized by chemical mechanicalpolishing and cleaned. Finally a “clean up” etch is applied and theresulting structure is cleaned.

FIG. 22 illustrates a next stage in the process, in which a patternedconductive layer 250 is formed in contact with the plugs over the filllayer, providing bit lines and other conductors for the memory device,yielding the structure shown and described above with respect to FIG. 3.In embodiments of the process, a copper alloy damascene metallizationprocess is used in which the patterned conductive layer is formeddepositing fluorosilicate glass (FSG) on the exposed surface, and thenforming a photoresist pattern in the pattern desired. An etch is appliedremoving exposed FSG, and then liner and seed layers are deposited inthe pattern. Then, copper plating is applied to fill the pattern. Afterplating, an anneal step is applied, followed by a polishing process.Other embodiments can use standard Al—Cu processes, or othermetallization processes known in the art.

Other techniques for implementing a narrow bridge of memory material areshown in our prior U.S. patent application Ser. No. 11/155,067, entitledTHIN FILM FUSE PHASE CHANGE RAM AND MANUFACTURING METHOD, filed 17 Jun.2005, which is incorporated by reference as if fully set forth herein.

Most phase change memory cells known to applicant are made by forming asmall pore filled with phase change material, and top and bottomelectrodes contacting the phase change material. The small porestructure is used to reduce the programming current. This inventionreduces programming current without formation of the small pore,resulting in better process control. Furthermore, there are no topelectrodes on the cell, avoiding some possible damage of the phasechange material from processes used to form the top electrode.

A cell described herein comprises two bottom electrodes with adielectric spacer in between and a bridge of phase change material onthe top of the electrodes spanning across the spacer. The bottomelectrodes and dielectric spacer are formed in an electrode layer overfront-end-of-line CMOS logic structures or other function circuitstructures, providing a structure that easily support embedded memoryand function circuits on a single chip, such as chips referred to assystem-on-a-chip SOC devices.

Advantages of an embodiment described herein include that the phasechange happens on the center of the bridge over the dielectric spacer,rather than on the interface with an electrode, providing betterreliability. Also, the current used in reset and programming is confinedin a small volume allowing high current density and resultant localheating at lower reset current levels and lower reset power levels. Thestructure in embodiments described herein allows two dimensions of thecell to be defined by thin film thickness, achieving better processcontrol at nanometer scales. Only one dimension of cell can be definedby a lithographic process using a trimmed mask layer, which avoids morecomplex shrinking techniques.

While the present invention is disclosed by reference to the preferredembodiments and examples detailed above, it is to be understood thatthese examples are intended in an illustrative rather than in a limitingsense. It is contemplated that modifications and combinations will occurto those skilled in the art, which modifications and combinations willbe within the spirit of the invention and the scope of the followingclaims.

1. A method for manufacturing a memory device, comprising: forming anelectrode layer, the electrode layer including a first electrode and asecond electrode, and an insulating member between the first and secondelectrodes, the first and second electrodes having top surfaces exposedat a top surface of the electrode layer, the insulating member extendingabove the top surfaces of the first and second electrodes to form aninsulating wall, and the insulating member has a width between the firstand second electrodes at the top surfaces of the first and secondelectrodes; forming a bridge of memory material on the top surface ofthe electrode layer across the insulating member, the bridge comprisingfirst and second pads of thermally insulating material contacting thetop surfaces of the first and second electrodes respectively, and astrip of memory material extending between the first and second pads,the bridge defining an inter-electrode path between the first and secondelectrodes across the insulating member having a path length defined bythe width of the insulating member, wherein the memory material has atleast two solid phases.
 2. The method of claim 1, wherein said forming abridge includes forming the strip with a width about 50 nm or less and athickness about 50 nm or less.
 3. The method of claim 1, wherein saidforming a bridge includes forming the strip with a width about 20 nm orless and a thickness about 20 nm or less.
 4. The method of claim 1,wherein said forming a bridge includes forming the strip with athickness of about 10 nm or less and a width of about 10 nm or less. 5.The method of claim 1, wherein the width of the insulating member at atop surface of the wall of insulating material is less than 20 nm. 6.The method of claim 1, wherein said forming an electrode layer includesdefining a plurality of pairs of first and second electrodes, andisolation members separating a pair in the plurality of pairs fromanother pair in said plurality of pairs.
 7. The method of claim 1,wherein said forming an electrode layer includes defining a plurality ofpairs of first and second electrodes, in which two electrode membersacting as said first electrodes in respective pairs, share a thirdelectrode member arranged between said two electrode members; the thirdelectrode member being separated by insulating members from said twoelectrode members, whereby two pairs of first and second electrodes inthe plurality of pairs are provided with their second electrodes in thethird electrode member, and further including defining isolation membersseparating said two pairs in the plurality of pairs from other pairs insaid plurality of pairs.
 8. The method of claim 1, wherein said formingan electrode layer includes: forming a dielectric layer on a substrate;forming a first conductive layer on the dielectric layer; etching thedielectric layer and the first conductive layer to form stacks, thestacks having sidewalls; forming sidewall dielectric elements on thesidewalls of the stacks; forming a second conductive layer over thestacks and the sidewall dielectric elements; planarizing the secondconductive layer, the stacks, and the sidewall dielectric elements toform a substantially planar top surface and to expose the sidewalldielectric elements, wherein the sidewall dielectric elements act as theinsulating member; and etching the remaining portions of the first andsecond conductive layers from the substantially planar top surface toprovide the top surfaces of the first and second electrodes, so thatwalls of insulating material extend above the top surfaces of the firstand second electrodes.
 9. The method of claim 8, wherein saidplanarizing comprises chemical mechanical polishing.
 10. The method ofclaim 1, wherein said forming a bridge includes: forming a layer ofmemory material on the electrode layer; patterning the layer of memorymaterial to define a strip of memory material over the electrode layer;and patterning the strip of memory material to define said first andsecond pads and said strip of the bridge.
 11. The method of claim 1,wherein said forming a bridge includes: forming a layer of memorymaterial on the top surface of the electrode layer; forming a layer ofresist material over the layer of memory material; patterning the layerof resist material using a lithographic process to define a stripe stripof resist material; trimming the width of the strip of resist materialto define a more narrow strip of resist material over the layer ofmemory material; etching the layer of memory material which is notprotected by the more narrow strip of resist material to form a stripeof memory material; and patterning the strip of memory material todefine said first and second pads and the bridge.
 12. The method ofclaim 1, including forming a patterned conductive layer over saidbridge, and forming a contact between said first electrode and saidpatterned conductive layer.
 13. The method of claim 1, wherein thememory material comprises an alloy including a combination of Ge, Sb,and Te.
 14. The method of claim 1, wherein the memory material comprisesan alloy including a combination of two or more materials from the groupconsisting of Ge, Sb, Te, Se, In, Ti, Ga, Bi, Sn, Cu, Pd, Pb, Ag, S, andAu.
 15. A method of manufacturing a memory device, comprising: forming afirst conductive layer on a dielectric layer; etching the firstconductive layer and the dielectric layer to form a stack; forming asidewall dielectric element on a sidewall of the stack; depositing asecond conductive layer over the stack and the sidewall dielectricelement; etching the first and second conductive layers to make firstand second electrodes separated by the sidewall dielectric element toexpose a top surface of the sidewall dielectric element and , whereintop surfaces of the first and second electrodes are lower than the topsurface of the sidewall dielectric element so that the sidewalldielectric element has a top surface at a level higher than the topsurfaces of the first and second electrodes; and forming a memoryelement in contact with the top surfaces of the first and secondelectrodes and extending across the top surface of the sidewalldielectric element wherein the top surface of the sidewall dielectricelement is higher than the top surfaces of the first and secondelectrodes.